SPC 1200Z Day 1 Outlook

Day 1 Outlook Image

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1133 PM CST Fri Nov 06 2020

Valid 071200Z - 081200Z


A few strong wind gusts may accompany thunderstorms across parts of
southeast Arizona later this afternoon and early evening.

...Southeast AZ/southern CA...

Strong upper low is digging southeast along the central CA Coast
late this evening. A significant piece of this feature is forecast
to dig into the lower CO River Valley by 08/00z as 100kt+ 500mb
speed max translates across the northern Baja Peninsula before
ejecting into eastern AZ during the late evening. Substantial 12
hour mid-level height falls will develop ahead of this short wave,
and the frontal zone that surges across the southwestern US will be
sharply focused/forced in response.

While boundary-layer moisture is currently limited across the
southwestern deserts, surface dew points are notably higher south of
the international border. Low-level trajectories will become more
favorable for some of this moisture to advance north ahead of the
front. If adequate moisture can return to southeast AZ ahead of the
wind shift, scattered robust convection could develop. Latest CAMs
support at least isolated thunderstorm activity and forecast
soundings favor gusty winds given the steep lapse rates and strong
flow that will spread across this region. Although SBCAPE will not
be that significant, vertical mixing and fast storm motions will
favor gusty winds. For these reasons have introduced 5 percent wind
probabilities with thunderstorms that develop ahead of the cold
front. This activity will spread rapidly northeast into northwest
NM/south-central CO, possibly in the form of a weak squall line.
Given the limited buoyancy it's not clear the threat of damaging
winds will extend into this region.

Upstream across southern CA, very cold mid-level temperatures will
overspread this region by 18z. Forecast soundings near the southern
CA Coast exhibit SBCAPE near 450 J/kg within this post-frontal
regime. While severe hail is unlikely, profiles appear favorable for
at least small hail within the strongest updrafts.

..Darrow.. 11/07/2020

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